fix(admissions): state distance in miles throughout, never mixed

The postcode check read "69 m away — inside the September 2026 cut-off of
0.17 miles". Both numbers are right and the sentence is still useless: the
reader has to convert one of them to check a comparison we had already made
for them.

The cause was a readability rule of mine in formatCutoffDistance, which swapped
to metres below 100m on the grounds that "0.04 miles" carries less than "69 m".
Taken one figure at a time that holds. Taken in a sentence containing two
figures it guarantees a mismatch whenever they fall either side of the
threshold — and a 270m cut-off with a nearby home does exactly that.

Miles now lead everywhere. It is the unit UK school admissions runs on:
councils publish cut-offs in miles (90% of the collected source rows), and it
is what a parent has already been quoted in their booklet and offer letter.
The metric figure survives only as support beside the miles figure on the
Admissions tile, where it converts the same value rather than presenting a
second one to compare.

Below 0.01 miles the decimal places run out rather than the unit being wrong,
so a very short distance is described — "under 0.01 miles" — instead of
rounding to a flat "0.00 miles", which would read as no distance at all.

Both figures in the verdict now go through one formatter with no fallback that
could reach for another unit. The old `?? "N m"` fallbacks on that line were a
second route to the same defect and are gone.

Covered by a sweep over sixty home/cut-off combinations spanning the old
switch point, asserting no verdict contains a metric reading and that exactly
two miles figures appear; plus the reported case pinned verbatim, and an e2e
guard on the rendered verdict.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01WDvkyqqHABm4bmth2kjAxE

nextjs-app/components/school/lastDistanceOffered.ts

@@ -16,7 +16,7 @@
  */
 
 import type { SchoolAdmissionDistance } from '@/lib/types';
-import { formatCutoffDistance, formatEntryYear } from '@/lib/utils';
+import { formatCutoffDistance, formatMiles, formatEntryYear } from '@/lib/utils';
 
 export interface CutoffDisplay {
   /** Headline figure, e.g. "0.31 miles". */
@@ -108,8 +108,13 @@ export function compareToCutoff(
   const verdict: CutoffVerdict =
     Math.abs(margin) <= CUTOFF_UNCERTAINTY_M ? 'too-close' : margin > 0 ? 'inside' : 'outside';
 
-  const label = formatCutoffDistance(distanceM)?.primary ?? `${Math.round(distanceM)} m`;
-  const cutoffLabel = formatCutoffDistance(cutoffM)?.primary ?? `${Math.round(cutoffM)} m`;
+  // Both sides through the same formatter, with no fallback that could reach
+  // for a different unit: the sentence compares these two numbers directly, so
+  // they have to be in the same one. formatCutoffDistance returns null for a
+  // zero or negative figure, and its old "N m" fallback here was one of the
+  // ways a metres reading used to appear next to a miles one.
+  const label = formatMiles(distanceM);
+  const cutoffLabel = formatMiles(cutoffM);
 
   // "the September 2026 cut-off of 0.17 miles" rather than "the 0.17 miles
   // cut-off for September 2026": the figure carries its own unit word, which